Vacuum switch



Y April 21, 1970 D. R. BELLIS 3,508,021

' VACUUM SWITCH Filed Jan. 5, 1967 3 Sheets-Sheet 1 INVENTOR.

00171410 R Bill /5 April 21, 1970 R, Lus 3,508,021

I VACUUM SWITCH Filed Jan. 5, 1967 67 3 Sheets-Sheet 2 INVENTOR. DOA/ALB'R BHl/S April 21. 1970 ,D. R. mus 3,508,021

VACUUM. SWITCH Filed Jan. 5, 1967 5 Sheets-Sheet s I 2 l3 l7 95INVENTOR.

0044410 A BfZl/S I ATTYS United States Patent 3,508,021 VACUUM SWITCHDonald R. Bellis, 'Coeur dAlene, Idaho, assignor to Vacuum PowerComponents, Inc., CoeurdAlene, Idaho, a corporation of Idaho Filed Jan.3, 1967, Ser. No. 606,776 Int. Cl. H01h 33/66 US. Cl. 200-144 14 ClaimsABSTRACT OF THE DISCLOSURE The disclosure describes a preferredembodiment of my invention concerning a vacuum switch comprising ahousing having an annular metallic or conductive section and aninsulating or nonconductive section 11. An inwardly directed bafllestructure is positioned substantially across the housing adjacent to thejoinder of section 11 and 12. The nonconductive section 11 has anannular wall 16 formed of glass or ceramic material. The switch has astationary contact assembly 21 and an opposed movable contact assembly22 that are mounted to the end walls 13 and 17 respectively. Thestationary contact assembly 21 has a terminal rod 23 with an axialcavity 37 formed therein offset from the longitudinal axis of theswitch. The movable contact assembly 22 has a terminal rod 27 alignedand opposed to rod 23. Rod 27 has an axial cavity 38 formed therein thatis offset from the longitudinal axis and diametrically opposite cavity37. Contacts 24 and 29 are mounted on the adjacent ends of the rods 23and 27 respectively. A passageway 42 is formed in rod 23 communicatingwith the cavity 37 and the exterior of the rod. A post 40 of getteringmaterial is positioned in the cavity 37.

My invention relates to vacuum switches and more particularly to vacuumswitches that are capable of being used as circuit breakers carryinghigh current loads.

One of the objects of my invention is to provide a new vacuum switchthat is etficient in operation, simple in construction and economical tomanufacture.

An additional object of my invention is to provide a new vacuum switchthat has increased longevity and reliability.

A further object of my invention is to provide a vacuum switch that iscapable of operating with increased current ratings.

An additional object of my invention is to provide a novel vacuum switchstructure that minimizes thedepositing of metallic material on theinsulator.

A further object of my invention is to provide a vacuum switch for useas a circuit breaker in which the movable portion of the switch has arelatively small mass to enable the switch to operate faster.

An additional object of my invention is to provide a vacuum switch thatis capable of shifting the location of the me across the switch contactsin order to reduce the erosion of the contacts.

A further object of my invention is to provide a novel vacuum switchstructure for shielding the insulator from the metallic vapors generatedby the arcing.

An additional object of my invention is to provide a novel applicationof gettering material within the switch will "ice showing the principalelements of a preferred embodiment of my invention;

FIG. 2 is a cross sectional view of a vacuum switch showing certainmodification of the preferred embodiment;

FIG. 3 is a cross sectional view of a vacuum switch showing certainmodification of the preferred embodiment in which a baflle' shield issupported by the insulator spaced from the conductive elements of theswitch; and

FIG. 4 is an artistic perspective view showing the electrical contactsof the vacuum switch emphasizing the magnetic field pattern around thecontact eleme'nts.

FIRST EMBODIMENT OF VACUUM SWITCH FIGURE 1 illustrates in cross sectionthe details of a first switch embodiment incorporating the basicelements of my invention. The electrical contact assemblies are enclosedwithin a sealed housing comprising a conductive annular section or wallmade from metallic material generally designated by the numeral 10 andnonconductive or insulating section or wall generally designated by thenumeral 11. An arc chamber 12, wherein arcing is confined during openingof the contact assemblies, includes the conductive annular section 10sealed at one axial end to an end metallic wall 13. The remaining end ofsection 10 is sealed at 14 to the adjacent open end of the nonconductivesection 11. Any conventional seal might be used between the joinedconductive members or between the conductive members and thenonconductive members. As illustrated, the metal to metal seals wouldmost likely be brazed, and the metal to insulation seals would be formedby embedding metal connecting strips in the glass insulator structure asit is being formed.

The are chamber 12, whose interior is open to the insulating section 11,is substantially enclosed by an inwardly directed bafile structure 15 tothe joinder of the insulating section 11 and arc chamber 12. In FIGURE 1the baffle 15 is shown as a metallic wall inwardly directed from theopen axial end of the wall 12. It is the area enclosed by the walls 10,13 and 15 which is generally referred to herein as the arc chamber.

The insulating section 11, formed adjacent to the arc chamber 12,comprises an annular wall 16 formed of glass or ceramic material sealedrespectively to the arc chamber 12 at 14 to a second end wall 17 at 18.The wall 17 is axially spaced from wall 13, and the area lying betweenthese end walls defines the axial limits of the vacuumized enclosure.Air is evacuated through a tube 20 extending through an aperture formedin end wall 17. The tube 20 is pinched off to seal the evacuatedenclosure.

The electrical contact assemblies used in the switch shown in FIGURE 1are generally designated by the numerals 21 and 22. The contact assembly21 is stationary while the contact assembly 22 is movable between afirst position in abutment with contact assembly 21 and a secondposition displaced axially therefrom.

The stationary contact assembly 21 includes a post or rod 23 fixed tothe end wall 17. The rod 23 protrudes outwardly through wall 17 and itsouter end comprises a first electrical terminal for the switchcomponents. A radially enlarged contact 24 having a plane contactsurface 25 is affixed to the inner end of rod 23. Rod 23 also supportsan annular baflle 26 located outwardly adjacent to bafile 15 and thejoinder of sections 10 and 11; the baffles 15 and 26 overlapping oneanother so as to provide a circuitous route to minimize escape ofmetallic vapor from within the arc chamber 12.

The movable contact assembly 22 incldues a supporting post or rod 27slidably guided by end wall 13 within an inwardly projecting bearing 28and serves as the second electrical terminal for the switch. Rod 27 isaligned axially with rod 23 and is carried by bearing 28 for slidingmovement parallel to the longitudinal axis of the switch. At its innerend it carries a radially enlarged contact 29 having a plane contactsurface 30 complementary to the contact surface 25 previously described.The integrity of the vacuum within the enclosure is maintained by aflexible vacuum tight sealing means or bellows 31 having one end sealedat 32 to the rod 27 and having its remaining end sealed at 33 to the endwall 13. The bellows 31 is partially enclosed within a protectiveannular cover 34 fixed to rod 27 and movable in unison with it.

The switch is adapted to 'be mounted in a fixed position by 'means ofthree equally spaced lugs 35 which protrude outwardly from end wall 13and which are centered about the axis of posts 23 and 27. The outer endof rod 27, which protrudes outwardly from end wall 13, is threaded at 36to provide a mechanical connection to a suitable device (not shown) foropening or closing the contact assemblies as might be necessary in theapplication to which the switch is directed.

The contacts 24 and 29 are preferably fabricated of tungsten and copper,utilizing available compositions wherein the tungsten is porous, havingits voids filled with copper. Such a composition is obtainable withextreme metal purity annd essentially no gaseous content.

It should be noted that the movable contact assembly 22 as shown inFIGURE 1 has a relatively small mass as compared to circuit breakerspresently available. The small mass permits faster operation of theswitch and allows the moving elements to be mechanically shifted by arelatively smaller force being applied by the mechanism that moves post27 The are chamber 12 confines any are momentarily directed across thecontacts 24 and 29 as they are opened. Metallic vapors produced by suchan arc will condense or be deposited on the surfaces of the members 10,13, and 26 so that no substantial amount of such products will bedeposited on the inside surface of the insulating wall 16. Such anarrangement increases the longevity and reliability of the switch.

The design of rods 23 and 27 as shown in FIGURE 1 incorporates twoadditional features of importance of my basic invention. The first ofthese is provision for a moving magnetic field to prevent concentrationof an arc across contacts 24 and 29 in any one particular location. Toaccomplish this, the inner end of rod 23 is provided with an axialcavity 37. The central axis of cavity 37 is radially offset from thelongitudinal axis of the rod 23, thereby making the cavity 37 eccentricrelative to the rod 23-. As shown, rod 27 is provided with a similareccentric cavity 38. Cavity 38 is illustrated as being offsetdiametrically opposite to cavity 37. In general, either one rod, or both(as illustrated), may be so formed to shift the center of theelectrically conductive mass of one or both rods adjacent to theirrespective inner ends.

The shift in the center of the electrically conductive mass of one orboth posts results in a shift in the magnetic field which will bedeveloped about the rods and contacts as electrical current passesthrough them. This feature will be discussed further in detail below,and for the present it is sufficient to state that the shifting magneticfield will result in continuous movement of the location at which an arebetween the two contacts will be directed relative to their rsepectivecontact faces.

An additional feature is illustrated on rod 23. This is the inclusion ofa post 40 anchored to the interior of contact 24 and extending withinthe cavity 37. Post 40 is preferably made of refractory metal such asmolybdenum or tantalum. A gettering material, such as Ceralloy(manufactured by -Ronson Metals Corp.) is sintered to post 40 to absorbgases in its surrounding environment. It is used to remove from theinterior of the enclosure any gaseous molecules which might be producedduring operation of the switch components. The interior of cavity 37 isin open communication with the interior of the arc chamber 12 by meansof an intersecting passageway 42 formed through rod 23. The side wallsof the gettering material on post 40 are spaced from the side walls ofcavity 37 so as to provide maximum surface exposure of post 40. Thelocation of the gettering assembly in cavity 37 serves to protect thisactive material from damage and contamination by metal vapors duringoperation (or arcing).

Since a gettering material as described absorbs gas more actively as itstemperature is increased, the removal of gas from the environmentsurrounding post 40 will be proportional to the severity of theelectrical load handled by the switch components. The supporting post 40is preferably a refractory metal having characteristics capable of hightemperature vacuum outgassing prior to application of getteringmaterial. Preferably this material should be molybdenum or tantalum,either of which introduces a slight delay in the time of maximumoperation of the gettering material, due their thermal conductivitycharacteristics. The action of the gettering material will therefore bemost effective at the time slightly after the opening of the contactassemblies, so that gaseous materials are most effectively removed afterextinguishing of the arc, when such materials will be most prominentwithin the arc chamber 12. The action of the gettering material servesto continually maintain the quality of the vacuum within the enclosureand thereby insures longer life for the switch than is possible inconventional vacuum switches without such provision.

The construction of the apparatus shown in FIGURE 1 permits the switchto be applied as a circuit breaker and recloser switch with desirableswitching characteristics particularly required in the design of larger,higher rated units. This structural relationship increases the longevityof the switch and reduces the normally high transient voltages whicharise during the circuit breaking operation in a vacuum environment.

The size and power capability of the switch can be extended by enlargingthe components making up the arc chamber 12 and insulating section 11.The metal components of the arm chamber 12 may be enlarged both indiameter and depth in order to accommodate larger electrical parts andto thereby increase its current handling ability. The insulator section11 might also be increased in wall thickness, diameter or length asrequired for higher voltage stand off. Larger units would probably beoriented vertically with the wall 13 serving as the lower supportingbase member. The combination of the metal are chamber and the insulatingsection provides greater versatility and capacity in this unit than ispossible in prior vacuum switches fully enclosed within a glass orinsulating envelope.

SECOND EMBODIMENT OF THE APPARATUS In FIGURE 2 is illustrated a modifiedsecond embodiment of the basic switch construction illustrated in FIG-URE 1. The switch shown in FIGURE 2 operates sequentially in a two stepoperation as opposed to the instantaneous opening of the solid contactsillustrated in FIGURE 1. In the case of the switch shown in FIGURE 2,initial movement of the movable contact opens only a portion of thecontact area and increases the effective electrical resistance of themovable contact assembly prior to complete opening thereof.

In the case of a vacuum switch used for making or breaking circuitshaving high electrical loads, the switch shown in FIGURE 2 hasadvantages over the simple two contact switch apparatus. Rapidinterruption of current often causes the generation of transientvoltages of great magnitude in equipment connected in the circuit. Thesehigh voltage transients can serious damage such equipment. The apparatusshown in FIGURE 2 is capable of preventing such transient voltages frombecoming of great magnitude by providing improved control of the rate ofdisconnection of the circuit. Specifically, this apparatus providesmeans for reducing the current in the circuit by a substantial degreeprior to complete opening of the circuit.

As seen in FIGURE 2, the basic features of the switch assembly aresimilar to that shown in FIGURE 1. The enclosure within which the switchis housed includes an arc chamber 42 and an insulating section 43. Theare chamber 42 is formed by a bell-shaped annular wall 44 leadinginwardly to a wall section 45 that is of a reduced diameter at its innerend. The reduced section 45 is joined to a cylindrical shell 46 ofinsulating material. The shell 46 is sealed to both the wall section 45and to an end wall 47. The metal wall member 44, 45 and 47 arepreferably made of an alloy having proper thermal coefiicient ofexpansion characteristics to match the insulating shell 46. In onepractical form of the apparatus, shell 46 is made of calciumaluminosilicate glass, such as that sold as -Cornings Code 1723. Amatching sealing metal such as low carbon molybdenum is used for hightemperature characteristics, and greater ductility, or a lowertemperature hard glass may be used with an alloy having matching thermalexpansion characteristics.

In this form of the invention, the stationary contact is mounted on theshorter of the two rods, the movable contact being in two parts andrequiring the longer bearing support. The stationary contact 48 has afirst contact surface 49a and a second contact surface 49b. The movablecontact includes an outer annular contact 50 and an inner circularcontact 51. The facing surface of contact'50 is complementary to thecontact surfaces 4% and the facing surface of contact 51 iscomplementary with the contact surface 49a.

The stationary contact 48 is supported by the end wall of thebell-shaped wall section 44 on a copper rod 52. Rod 52 includes an axialcavity 53 within which is mounted a post 54 having flashless getteringmaterial sintered to it in the manner previously described. The post 54is preferably a heat conductive ,post of tungsten or molybdenum.

The cavity 53 is intersected by a radial passageway 55 formed throughthe rod 52 so as to place cavity 53 in open communication with theinterior of arc chamber 42. In this manner, gaseous particles within arcchamber 42 can contact the gettering material on post 54 and therebyremoved.

Rod 52 is provided with a continuing aperture 56 in communication withcavity 53, leading to a copper tube 57 through which air is removed fromthe interior of the enclosure, the tube 57 being pinched to a closedposition after evacuation of the enclosure.

The stationary contact 48 and the inner movable contact 51 arepreferably made of porous tungsten with a filling of copper in the poresor voids of the material. The outer movable contact 50 is preferablymade of similar material having relatively lower electrical conductivityso as to furnish greater resistance to the flow of current that isfurnished by the material used in contact 48 and contact section 51.

The inner contact 51 is fixed to the inner end of an inner rod 58aligned coaxially with contact 48. The rod 58 is slidably receivedthrough a hollow outer rod 60 by means of bushings 61 and 62 at itsrespective outer and nner ends. Rod 60 is in turn slidably supported bya bearing 63 fixed to the end wall 47 in a sealed relationship. Themovable connection for rod 60 is sealed by a flexible stainless steelbellows 64 sealed at one end to bearings 63 and to its remaining end toa disc 65 fixed to rod 60. The connection between rod 60 and rod 58 issealed by a similar flexible bellows 66 sealed at one end to rod 60 andat its remaining end to rod 58. In this Way, the integrity of the vacuumwithin the enclosure is maintained despite the relative movementafforded between rods 58 and 60.

The outer end of rod 58 is provided with a threaded aperture 67 to whicha suitable device for moving the contacts can be mechanically connected.The rod 58 includes an annular shoulder 68 adjacent its outer endadapted to move axially between an outer shoulder 70 and an innershoulder 71 fixed to the hollow rod 60. It can thus be seen that themovement of rod 58 to the right in FIGURE 2 will first leave rod andcontact section 50 unmoved. After the inner rod 58 and contact section51 have moved the distance permitted prior to contact of shoulder 68with shoulder 70, continued movement of rod 58 will result in movementof rod 60 and contact 50 in unison with it, thus providing a lost motionconnection. Closing of the contacts will occur in precisely the oppositesequence. First, both contact 50 and 51 will move simultaneously untilthe contact section 50 abuts contact 48. Continued movement of rod 58will finally bring the contact 51 also in abutment with contact 48. Thissequence of operation is insured by proper design of the externaloperating mechanism (not shown).

This two step operation, when coupled with a proper choice of electricalconductive properties for the contact members, results in a momentaryincrease in the electrical resistance through the switch immediatelyprior to complete opening of the contacts. Assuming that the electricalconductivity of the outer movable contact 50 is less than that of theinner movable contact 51, the resistance of the switch will be increasedafter initial opening to the contact 51. This will reduce the magnitudeof current and voltage that the remaining contact 50 must operateagainst upon opening or separating from the stationary contact 48. Thisincrease in effective resistance of the contacts results in theprotection of the higher conductive contact 51 from erosion by arcing.Furthermore, the magnitude of recovery voltages and the time duringwhich the voltages shall rise in equipment in a power circuit includingthis switch following interruption of current will be reduced due to theincreased resistance of the switch introduced during its operation.

In this form of the apparatus, the arc chamber 42 is physicallyseparated from the insulating section 43 by a radial baflle 72 extendingoutwardly from the post 60. The barrier 72 is in outward juxtapositionwith the reduced wall section 45 so as to substantially enclose the arcchamber 42 when the contacts are in their closed positions. Barrier 72serves to protect the insulating section 43 of the enclosure frommetallic vapors that might be released during arcing caused by openingof the contacts.

MOVEMENT OF AN ARC IN A VACUUM CIRCUIT BREAKER terrupter in a powercircuit, an arc may occur resulting in continued current flow betweenthe contacts of the device as the contacts open and move apart. Such anarc normally originates from and continues to flow between cathode andanode spots on the two contacts. With a conventional contact, these arcspots are normally confined to a small part of the available contactarea and the power concentration at such small areas generates extremelyhigh local temperatures. Resulting in vaporization due to the hightemperatures creates a plasma which in turn supports the arc. To reducethese temperatures, it is advisable to prevent the arc spots fromdwelling at any one location on the contacts.

In FIGURE 4 is illustrated the general structure by which the cathodeand anode spots of such an arc can be maintained in motion. The rodwhich carries the stationary contact 82 is shown with an eccentric axialcavity 81 formed through it adjacent to the contact 82. The movable rod83 has a similar cavity 84 adjacent to the movable contact 85. The heavycurrent that flows through the switch during fault conditions causes anunsymmetrical electromagnetic field to exist in the region aboutcontacts 82 and 85 when these contacts are carrying electrical current.A similar phenomena could be obtained by the use of any number ofdifferent physical configurations of the conductors which would cause itto be asymmetrical, or by placing a material of high magneticpermeability about the conductor in an asymmetrical manner.

The magnetic force fields generated about rods 80 and 82 by the currentflowing through them are asymmetrical with respect to the centrallongitudinal axis of rods 80 and 83. In addition, since the cavities 81and 84 are diametrically opposed, the fields are further disorientedwith respect to the general axis of the arc path between contacts 8'2and 85. This distorted magnetic force field, illustrated statically inFIGURE 4 and designated by the numeral 86, reacts with the fields of theions and electrons in motion in the arc plasma during opening of thecontact to cause a displacement of the arc from its normal path,resulting in movement of the arc spots on the surfaces of contacts 82and 85. Because of the dynamic nature of the arc and the varying natureof the power line current flowing through the switch, plus oscillatorycurrents in most interrupting operations, the asymmetrical magneticforce field will also be dynamic and constantly changing. This movementwill maintain the arc spots in continuous movement until the arc isfinally extinguished. The movement will be random and will prevent thearc from concentrating on any particular area of the contact surfaces.

To make best use of the displaced magnetic fields, the conductors shouldbe constructed in a manner so as to place the asymetry in proximity tothe switch contacts. Furthermore, the displaced electrical axis (andconsequently the displaced magnetic fields) of the two conductors thatsupport the contacts may be arranged so that they are not in coaxialalignment. This displacement (FIGURE 4) provides a twisting toroidalmagnetic field in the space about the two contacts. The magnetic fieldabout the rods 80 and 83 is shown in FIGURE 4 as it would exist understatic conditions with the contacts 82 and 85 closed and with directcurrent flowing through the electrodes. It is to be noted that theelectromagnetic lines of force 86 are both axially displaced andangularly distorted in the area adjacent to the contacts. Phase changeswould cause rotation of the twisted magnetic fields and amplitudechanges would cause variation in its strength. As the contacts opened,this dynamic picture would be increasingly complex, and would beconstantly changing in an irregular pattern.

An electrical arc in such a moving magnetic environment would be forcedto move and would be prevented from concentrating on an initial orfavorable hot cathode spot. This is true because of theconductive natureof the gas that is present even in high vacuum environments, to supportany electrical arc. Such a gas is highly ionized and will encounterforces which tend to move it in a direction normal to the movingmagnetic field. The are supported by these particles will be moved as aresult.

The general structure for moving the are between the contacts isincorporated directly in the switch shown in FIGURE 1 as described aboveand can be readily applied to any modification of this general switchstructure, such as that shown in FIGURES 2 and 3. The application ofthis structure is not limited to any physical configuration of thecavities, rods or contacts, and can apply to a wide variation ofstructural requirements relating to many switch applications.

THIRD SWITCH MODIFICATION In FIGURES 1 and 2 the two chambered structureis shown with an inwardly directed wall supported by the metal wallsection of the arc chamber adjacent to its inner end. In FIGURE 3 isillustrated a slight modification of the switch structure shown inFIGURE 1. In this instance, the structure relating to the contactassemblies 21 and 22 is unchanged and similar reference numerals areused to designate the parts as shown. The cylindrical wall 10' is shownin sealed contact with the inner end of an insulating wall section 16'.The wall section 16' is sealed to an end wall 17 and the metal wallsection 10 is sealed to an end wall 13'.

In this instance, a metallic shield is shown mounted on the insulatingsection 16. The baffle shield 90 includes a cylindrical wall thatextends to an area adjacent to the end wall 13. The shield 90 issupported by an interior annular groove 91 formed about the insulatingsection 16', the shield 90 including a cooperating exterior shoulder orprojection 92. At its inner end, shield 90 extends inwardly at 93 to alocation adjacent to the contact posts extending through the insulatingsection 16.

This shield 90 serves the same basic purpose as the inwardly directedwall sections and baffles mounted on the posts and shown in FIGURES land 2. That is, it mechanically deflects or collects particles emittedin the arc chamber during opening of the contacts. This preventscollection of metallic particles on the interior of the insulatingchamber 16. However, the electrical properties of shield 90 areditferent from those of the baffles and wall sections previouslydescribed. The shield 90 will be floating on potential in that it issupported only by the insulating part of the vacuum enclosure. Theadvantage of this floating potential is that during operation of theswitch it is not fixed in potential equal to either one electrode or theother. During operation of the moving contacts in interrupting thecurrent of an electric circuit, the floating baflle will tend to assumea potential determined by the nature of the arc vapors that strike it.This will vary from one operation to another being principally dependentupon the amplitude of the current being interrupted.

When the switch is open and the electric connections are energized, theshield 90 will be either at approximately one quarter or three quartersof the line potential, depending upon the manner in which the device isconnected in the line. When the switch is closed with normal linecurrent flowing through it, there will be no significant difference inpotential between the shield 90 and the switch contacts. The manner ofmounting the shield 90 on the inside surface of the insulating section16' takes full advantage of the high resistance to voltage breakdownafforded by the vacuum environment within the enclosure. The shield doesnot extend through the insulator to the exterior of the enclosure whereatmospheric pressure conditions might allow arcing or high voltagetracking to occur. The potential at the shield 90 is structurallyinsulated from the exterior of the enclosure. Obviously, this structurecould be equally well applied to the apparatus shown in the secondembodiment of the switch (FIG- URE 2).

Many combinations of the specific features set out above and manyobvious substitutions of equivalent structures will readily presentthemselves to one skilled in the art. Therefore, only the followingclaims are intended to define my invention.

Having thus disclosed my invention, 1 claim:

1. In a vacuum switch:

(a) an annular vacuumized housing comprising:

( 1) an electrically conductive section;

(2) an electrically non-conductive section joined to the conductivesection; and

(3) electrically conductive end caps;

(b) an electrically conductive baffle structure mounted within thehousing, extending substantially there across adjacent to the joinder ofthe conductive and non-conductive sections for defining, in spacedrelation with the electrically conductive section, an arc chamber forrestricting metallic vapor movement from thearc chamber to theelectrically nonconductive section;

(c) a stationary contact assembly mounted to one of the end caps, saidstationary contact assembly comprising a stationary rod that has one endthereof extending into the arc chamber;

(d) a movable contact assembly slidably mounted in the other end cap,said movable contact assembly comprising a rod with one end thereofextending into the arc chamber, adjacent the stationary rod end; and

(e) a flexible sealing means connected between the movable contactassembly and the other end cap for maintaining a vacuum in the housingfor allowing movement therebetween;

(f) the stationary and the movable contact assemblies being alignedalong a common longitudinal axis; at least one of the rods having anaxial cavity formed therein offset from the longitudinal axis, forasymmetrically displacing the magnetic fields generated by the contactrods.

2. The combination in accordance with claim 1 whereaxial cavities areformed in the adjacent ends of both rods with the cavities being offsetfrom the longitudinal axis and from each other.

3. The combination in accordance with claim 2 wherein the axial cavitiesare located diametrically from each other.

4'. The combination in accordance with claim 1 further comprising:

electrical contacts mounted on the adjacent ends of the rod for engagingeach other when the switch is closed.

5. The combination in accordance with claim 4 whereelectrical contactsare radially enlarged from the rods and have facing contact surfacescomplementary to each other adapted to provide surface to surfacecontact when the switch is closed.

6. The combination in accordance with claim 4 further comprisinggettering material positioned in the axial cavity.

7. The combination in accordance with claim 6 wherein the getteringmaterial is in the form of a post that is mounted in the cavity spacedfrom the rod.

8. In a vacuum switch encased by an annular housing positioned about thelongitudinal axis of the switch:

(a) a stationary contact assembly mounted to the housing comprising astationary rod extending along the longitudinal axis with an axialcavity formed therein offset from the longitudinal axis;

(b) a movable contact assembly mounted in the housing comprising amovable rod extending along the longitudinal axis opposing and spacedfrom the stationary rod; and

(c) a flexible sealing means connected between the movable contactassembly and housing for maintaining a vacuum within the housing whilepermitting movement therebetween.

9. The combination in accordance with claim 8 wherein the movable rodhas an axial cavity formed therein ofiset from the longitudinal axis anddiametrically op posite the stationary rod axial cavity.

10. The combination in accordance with claim 9 wherein at least one ofthe rods has a passageway formed therein communicating with the cavityand the rod exterior.

11. The combination in accordance with claim 10 wherein getteringmaterial is positioned within the cavity.

12. The combination in accordance with claim 11 wherein the getteringmaterial is in the form of a post positioned within the cavity spacedfrom the rod.

13. The combination in accordance with claim 8 wherein the contactassemblies further comprise electrical contacts mounted to the adjacentends of the rods, said contacts having facing surfaces complementary toeach other and adapted to make surface to surface contact when theswitch is closed.

14. The combination in accordance with claim 1 wherein the bafilestructure is in the form of a disc that is supported on one of the rods.

References Cited UNITED STATES PATENTS 3,174,019 3/1965 Jansson 200146 X3,239,635 3/1966 Baude 200-146 X 2,892,911 6/1959 Crouch 2001443,090,852 5/1963 Greenwood 200144 3,158,719 11/1964 Polinko et a1200-144 3,178,542 4/1965 Jennings 200144 3,211,866 10/1965 Crouch et a1.200144 3,283,100 11/1966 Frink 200144 3,372,258 3/ 1968 Porter 200144OTHER REFERENCES Classification Definitions, class 200, pp. 200-16,dated August 1957.

ROBERT S. MACON, Primary Examiner US. Cl. X.R.

